Advanced Gas Foil Bearing Design for Supercritical … Library/Events/2016/utsr/Wednesday...Advanced...
Transcript of Advanced Gas Foil Bearing Design for Supercritical … Library/Events/2016/utsr/Wednesday...Advanced...
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Peter A. Chapman, Jr., P.E.Principal Engineer
Mechanical Solutions, [email protected]
Albany, NYWhippany, NJ
Denver, COwww.mechsol.com
973-326-9920
2016 University Turbine Systems Research WorkshopNovember 1-3, 2016
Blacksburg, VA
Advanced Gas Foil Bearing Design for Supercritical CO2 Power Cycles
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Today’s Presentation
Project Background Overview of foil bearings:
A primer on various types, typical applications, etc.
Application in sCO2 Power Cycle MachinesDesign Considerations:Fluid propertiesMaterial selectionLoad Capacity, DampingPower Loss
Progress to Date Ongoing Work
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Project Background
Funding provided by the Department of Energy (DOE) Office of Fossil Energy Phase 1: June 2015 – March 2016 Phase 2: August 2016 – July 2018
Goal: develop a reliable, high performance foil bearing system using sCO2 as the working fluid Temperatures up to 800°C Pressures up to 300 bar
Key elements of the design: An advanced hydrostatically-assisted hydrodynamic foil bearing with higher
load capacity An integral gas delivery system to distribute flow throughout the bearing Addition of overload protection to handle large shaft excursions during
severe system transients Use of high temperature materials and coatings to prolong life and enabling
sufficient start/stop cycles
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High speed Extreme-temperature and/or oil-less environment Permits a hermetically-sealed system (eliminate
end seals) Insensitive to system pressure Applicable to high energy density turbomachineryMotors and generators are being designed to
run faster and with more torque, with reduced size & weight
Direct drive is a trend Long, maintenance-free life
Why Foil Bearings?
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Bump Style Radial Foil Bearing with Preload
Smooth top/inner foil – one or several segments
Support foil contains cylindrical bumps One or several segments One or several layers Sometimes slotted for improved edge loading, misalignment tolerance, etc.
Unidirectional, with shaft rotating from free end to fixed end
Is a hydrodynamic bearing – gas or liquid film OK
Compliant – reduces the need for high dimensional accuracy & roundness
General Features of a Bump-Style Radial Foil Bearing
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Application Spectrum for Foil Bearings
Journal Bearing
Diameter (inches)
4
3
2
1
020 40 60 80 100 120 140 160 180
Rotor Speed (thousand of rpm)
ACM
ACM
Solar Chiller RVP Gas
Turbine
Turboexpander
Turbocharger
Heat Pump Compressor
Motor Blower
Cryocompressor
Test Spindle
Air Compressor
Auto Gas Turbines
High-Speed Motor
Turbocharger
Textile Spindles
- Size and speed being studied under this project
Proprietary Gas Turbine
Turbocompressors
Heat Pump Compressor
Blower
Blower
ORC Turbine Gen.
ACM = Air Cycle Machine
Anticipated envelope for sCO2 power cycles in the multi-MW class
4 - 6 inches
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Foil Bearings for Miniature Gas Turbine Engine
160,000 rpm 66 mm journal
diameter
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Journal Bearings
Combination Bearings
Thrust Bearings
Foil Bearings for Turbocompressor
180,000 rpm 16 mm journal
diameter
Radial Foil Bearing
Foil Bearing Sizes
Thrust Bearing
Journal BearingTop foil removed
Foil Bearings for Centrifugal Air Compressor
93 mm journal diameter 45,000 rpm
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Applying Foil Bearings to Supercritical CO2 Machinery
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CO2 Fluid Properties
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Source: National Institute of Standards and Technology (NIST)http://webbook.nist.gov/chemistry/fluid/
Above 200°C, viscosity increasesas temperature increases Characteristic of gases Insensitive to pressure
variations Similar to air
Below 200°C, viscosity decreases as temperature increases Characteristic of liquids Very sensitive to pressure
variations A potentially unstable thermal
condition Start-up sequence may be
critical for proper performance
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0 200 400 600 800
Visc
osity
(µPa
-s)
Temperature (°C)
Viscosity of CO2
5 MPa (vapor)10 MPa20 MPa30 MPaAir (1 atm)
Viscosity Hydrodynamic lubrication simplified by using the Reynolds equation Viscosity is the only property taken into account
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CO2 Fluid Properties
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Source: National Institute of Standards and Technology (NIST)http://webbook.nist.gov/chemistry/fluid/
As flow exits the laminar regime, density becomes an important parameter
Studies have shown a significant increase in power loss as pressure (density) increases (Bruckner and Dellacorte1, Milone2)
The additional power loss must be accounted for in overall system efficiency
The heat generated must be managed to avoid overheating and potential thermal instability
Density The more compressible the fluid, the more other fluid properties influence
bearing design
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Den
sity
(kg/
m3)
Temperature (°C)
Density of CO2
5 MPa (vapor)10 MPa20 MPa30 MPa
1. Bruckner, R.J. and DellaCorte, C., “Windage Power Loss in Gas Foil Bearings and the Rotor-Stator Clearance of High Speed GeneratorsOperating in High Pressure Carbon Dioxide Environments”, Supercritical CO2 Power Cycle Symposium, Rensselaer Polytechnic Institute, April29-30, 2009, Troy, NY.
2. Milone, D., "Windage and Gas Foil Bearing Losses in a Supercritical Carbon Dioxide Turbine Generator;" Supercritical CO2 Power CycleSymposium, May 24-25, 2011, Boulder, CO.
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Material Considerations - Strength
Strength of Several Nickel Alloys (Courtesy Haynes International, Inc.)
Inconel X-750 commonly used foil material High strength at elevated temperatures Good fatigue and corrosion resistance Available in a variety of foil thicknesses
René 41 a potential alternative
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Advanced Coatings
Under normal, steady-state operating conditions, there is no contact between the shaft and bearing
During start-up and shut-down, contact is inevitable This is most often the life-limiting aspect of foil bearings By energizing the hydrostatic feature, rubbing during
start-up/shut-down may be avoided
Characteristics of a good coating include Low friction Resistance to wear Good adhesion to the substrate
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Advanced Coatings
A number of high temperature coatings were previously evaluated up to 650°C, with promising results
The best candidates were then evaluated up to 800°C
A new family of coatings is starting to become available, known as Adaptive coatings, or “chameleon” coatings Named due to their ability to adapt to changing
temperature by preserving good tribological properties from 25°C to 1000°C
Due to higher expense and long lead times, these will be evaluated in Phase 2
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Bearing Performance
Project focused on developing a journal bearing Diameter: 63.5 mm (2.50 inches) Length: 44.5 mm (1.75 inches) Speed: 60,000 rpm D⋅N: 3.81 million
Phase 1 testing was performed in air
Estimated Hydrodynamic Load Capacity
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0 10000 20000 30000 40000 50000 60000
Load
Cap
acity
(lbf
)
Speed (RPM)
Journal Bearing Load Capacity vs. Speed in Air
2193204316427538649760
Temp(°C)
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15000
20000
25000
30000
35000
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45000
50000
0 10000 20000 30000 40000 50000 60000
Stiff
ness
(lbf
/inch
)
Speed (RPM)
Journal Bearing Stiffness vs. Speed in Air
KxxKyy
Estimated Stiffness under Constant Load
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Hydrodynamic Performance
Phase 2 testing will be in sCO2
Estimated Hydrodynamic Load Capacity
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Hydrostatic Performance
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Adding a hydrostatic component is one method of enhancing a gas foil bearing
Pressurized gas is injected directly into the bearing cavity
Hydrodynamic load capacity often limits gas foil bearing use in some equipment, particularly larger machines running at lower speeds
Supplementing load capacity and stiffness could enable broader use of gas foil bearings
3. Kumar, M., "Analytical and Experimental Investigation of Hybrid Air Foil Bearings," A Thesis submitted to the Office of Graduate Studies ofTexas A&M University, August 2008.
Source: Texas A&M University (Kumar3)
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Hydrostatic Performance
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MSI is studying a proprietary design using CFX (ANSYS, Inc.)
CFD Results of a Single Nozzle
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Hydrostatic Bearing Performance
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Generated Hydrostatic Force and Stiffness vs. Differential Pressure for the Journal Bearing
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Hyd
rost
atic
For
ce (l
b)
Differential Pressure (psi)
Hydrostatic Force in Air
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0 10 20 30 40 50 60St
iffne
ss (l
bf/in
ch)
Differential Pressure (psi)
Hydrostatic Stiffness in Air
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Hydrostatic Bearing Performance
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Same CFD model used to predict performance in sCO2 Nature of sCO2 required the use of a Real Gas
Properties (RGP) table Table consists of a matrix of fluid properties as a
function of pressure and temperature Unlike the air case, high flow velocities are not present
due to much higher density, tending to keep the Mach number low.
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Validation Testing
Static Testing – Hydrostatic BearingDynamic Testing – Hybrid Bearing
Coating Evaluation
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Static Testing – Hydrostatic Bearing
Prototype hybrid bearings were constructed for both static (zero speed) and high-speed (50,000 rpm) testing
The bearings were installed in MSI’s high-speed test rig Initial static load testing was conducted by varying the load,
applying supply pressure, and measuring the vertical levitation of the shaft
Stiffness was measured by incrementally changing the load and recording the change in shaft position
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0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
0.0012
0.0014
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Vert
ical
Lift
(inc
h)
Differential Static Pressure (psi)
6 lbf13.5 lbf21 lbf
AppliedLoad
Hydrostatic Lift vs. Applied Static Pressure
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Static Testing – Hydrostatic Bearing
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Air Supply Line
Test Load
Hybrid BearingHousing
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Dynamic Testing – Hybrid Bearing
The same test rig was used to perform high-speed testing to 50,000 rpm
A hybrid foil bearing was installed on the drive end A conventional foil bearing was installed on the opposite end Rotor weight: 17 kg (37 lbm) Rig is driven by an air turbine
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AIR TURBINEDRIVE
FOIL BEARINGHOUSINGS
17 kgTEST SHAFT
TRADITIONALFOIL BEARING
RADIAL BUMPERS
HYDROSTATIC-ASSISTSUPPLY PORTS
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Dynamic Testing – Hybrid Bearing
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MSI’s High Speed Foil Bearing Test Rig Installed in Test Cell
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Dynamic Testing – Results
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Synchronous Vibration
At 30k rpm the rig experienced very stable operation
Vibration levels were very low
30krpm, 0 psi.05
0
MilsRMS
Turbine End: X & Y Probes Thrust End: X & Y Probes
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0
MilsRMS
Turbine End: X & Y Probes Thrust End: X & Y Probes30krpm, 10 psi
Dynamic Testing – Results
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Sub-Synchronous Vibration
At 30k rpm the rig experienced very stable operation
Vibration levels were very low
As hydrostatic air pressure was added (10 psi), a small sub-synchronous vibration (~79 Hz) was present
The sub-synchronous vibration grew as pressure was increased to 15 psi, but diminished at 20 psi
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Advanced Coating Testing
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High Temperature Start/Stop Cycle Testing
DRIVE MOTOR
PILLOW BLOCKBEARINGS
TEST SHAFT
HOT BOX
TORQUE ARMW/ LOAD CELL
TEST BEARING
LOAD
Rig Capabilities Automatic start/stop cycling Constant applied load 17,000 RPM 650°C Continuous torque monitoring
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Start/Stop Cycle Testing
Sample Bearings and Test Shaft After Cycling
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100 Cycles, 20°C 500 Cycles, 540°C 500 Cycles, 650°C
100 Cycles, 20°C 500 Cycles, 540°C 500 Cycles, 650°C
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Start/Stop Cycle Testing - Results
Coating successfully passed the cycle testing Test shaft shows evidence of some coating transfer Shaft has appearance of a typical burnishing
operation No evidence of adhesive wear was found Test shaft measured 8 microns (0.0003 inch) of
wear (10% of bearing clearance) after initial room temperature run
No measurable wear after high temperature cycles Wear of the top foil was 3-5 microns
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Ongoing Work
Phase 2 Continue to optimize design and refine analytical
models incorporating both hydrostatic and hydrodynamic bearing behavior
Include intra-bearing interaction among the bearing foils
Generate both optimized and practical (in sCO2) journal and thrust bearing designs
Conduct bearing validation tests in sCO2environment at Sandia National Labs
Continue evaluation and improvement of high temperature, low-wear coatings
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Acknowledgment
This material is based upon work supported by the U.S. Department of Energy,Office of Science, Office of Fossil Energy, under Award Number DE-SC0013691.
Disclaimer
This report was prepared as an account of work sponsored by an agency of theUnited States Government. Neither the United States Government nor anyagency thereof, nor any of their employees, makes any warranty, express orimplied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or processdisclosed, or represents that its use would not infringe privately owned rights.Reference herein to any specific commercial product, process, or service bytrade name, trademark, manufacturer, or otherwise does not necessarilyconstitute or imply its endorsement, recommendation, or favoring by the UnitedStates Government or any agency thereof. The views and opinions of authorsexpressed herein do not necessarily state or reflect those of the United StatesGovernment or any agency thereof.
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Stop By Our PosterPeter Chapman 973-326-9920 ext. 144; [email protected]